Mammalian central neurons and avian muscle cells have been grown in tissue culture to study 1) immunohistochemically identified peptidergic neurons. 2) peptide synthesis by those neurons, and 3) the characteristics of specific receptors. Sensory and spinal neurons stain specifically for nerve-specific enolase, while non-neuronal cultured cells do not. Some of these neurons stain positively for either methionine- or leucine-enkephalin, substance P, or somatostatin. Enkephalinergic neurons can synthesize and release methionine-enkephalin when incubated with labelled methionine. Binding studies have deomonstrated the existence of several classes of receptor on cultured neurons including those for GABA, opioid peptides and benzodiazepines. Cultured muscle cells have functional acetylcholine receptors which, when activated, stimulate the influx of labelled Na ions. Pentobarbital blocks this flux at a site that does not discriminate between the two isomers. The results show the utility of using cultured nerve and muscle cells as model systems to study, with neurochemical techniques, the synthesis of endogenous substance and the characteristics of their receptors.